Currently, when collisions, rock-strikings and the like accidents happen to oil tankers, in case that the hull cracks, plenty of crude oil will flow out of the vessel causing the environment to be polluted. To reduce the occurrence of such accidents and relieve the damage due the same, the technical measures which can presently be adopted are: crude oil is stored in separate holds in an oil tanker; double-wall shells are sued for an oil tanker and the sheet thickness of the hull is increased.
During transportation, the impurities contained in crude oil itself will partly deposit in the oil holds, so they have to be scavenged at regular intervals that corresponding hold-scavenging equipment will be needed and certain sewage will be produced after scavenging.
It is required for the oil tanker in no-load state to have a certain amount of ballasting water, a specially provided ballasting water hold does not cause any pollution, but needs to occupy a part of effective loading space; if an oil hold is used to contain the ballasting water, the water will be polluted thus requiring a corresponding treatment apparatus to be provided.
An oil tanker can often make its single-way transportation because of its unitary function of oil transportation.